- layers -to reflecting metal



Patented Sept. 21, 1954 "METHOD OF APPLYING PROTECTIVE LAYERS T REFLECTING MET-AL SURFACE S 'Cornelis "iKorver, Eindhoven, Netherlands, -assigner: to Hartford National- Bank and Trust Company, Hartford, Conn., as trustee z N 0 Drawing. Application November 6, 1951, I Serial No.- 255,139

"Claims priority, application Netherlands December 5, 1950 "6 Claims. 1

'Ih-is inventionrelates to methods of apply -'-protective'layersto reflecting metal surfaces and to mirrors-manufactured with the use of said methods.

-It isknown to; provide areflecting' metal surface on a layen-of lacquer provided one rigid support, thus dispensing-with treatments otherconsist, forexample, of aluminium which, due to i itsconsiderable'reflecting power throughout the and of visible light is particularly suitable.

Wlternativelyf however; -other metals, e. g, silver, may be used. A suitable method of providing the reflecting metal iayerconsists in vaporizing metal in a vacuum.

Int-conjunction *With the requirements with respect to smoothness, hardness and thermal stability imposed on"the-support preferably a" lacquer capable of-being hardened by "heating (mufiling lacquer). is employed. Due to the heatingopera'tion necessary'for har'deningthe lacquer thoroughly,=residues.of solventsiaridzmoisture are vapour-ized from the layer of lacquer in order that stheyemaylnot later occasiontdamage to the re- J flecti-ng-metal surface provided thereon. As is known mufiling lacquers-.best-satisfy the requirements imposed.

It has, however, been found that such refiecting metal surfaces do not fulfil stringent requirements imposed with respect to durability, since they are relatively readily damaged by atmosphere influences, dust and handling. It has been suggested to enhance the durability of such reflecting metal surfaces by subjecting them to chemical treatment or by precipitation of quartz vapour on to the metal surface. For reflecting aluminium surfaces a known method is to form a protective layer by oxidizing the surface of the aluminium by electrical agency. When employing silver a protective layer may be formed by heating the mirror in an oxygen or hydrogen peroxide atmosphere.

However, these methods of applying a protective layer are expensive.

The invention consists of a method of applying a protective layer to a reflecting metal surface, provided, for example, by vapourization of metal in a vacuum, on a hardened thermo-setting layer of lacquer, and is characterized in that the refleeting metal surface is covered with a layer of a thermo-setting lacquer which is subsequently hardened at a temperature lower than that at which the layer of lacquer which serves as a base for the metal mirror was hardened. The

"expression lower temperature is to be understood to mean a temperature which is atleast 15" C. and preferably at least 25C., lower than the temperature at which the supporting layer --of lacquer was hardened.

'I'heprotectinglayer of lacquer is thin and in order to ensure thedesired adherence anddurability, a-mufliing lacquer is chosen for this purpose.

It was found that the reflecting surfacewas "liable to damage during theoperation of hardening the protective layer unless said lower temperature was used; presumably due to deformation of the supporting layer of lacquer, bubbles and fissures were formed in the metal layer, thus usually the reflecting surface remains undamaged whenmuffiing the protective layer of lacquer at 125 to 130 C. It is to be preferred toohoose thetemperaturestill lower, for example C.

-'In this event, however, the times duringwhich the article furnished with the reflecting surface -issi1bjected to the hardening temperature, are longer. Thus,'forexample, one'anda half hours -wouldbe-requiredto harden the lacquer at "C.

At 115 C. the time of hardening is still longer, for example, two hours.

To provide the protective layer of lacquer use may be made of a spraying method according to which an appropriate lacquer solution is sprayed on to the reflecting metal surface by means of a spray-gun. Preferably, however, the method is employed according to which a small quantity of lacquer solution is applied on to the reflecting metal surface which is subsequently rotated rapidly. This method permits a very thin layer of lacquer to be applied by which the whole surface of the metal mirror is covered. For use in this method and also for obtaining a very thin layer, the lacquer solution should not be too viscous. Preferably, a lacquer solution having a viscosity of 9 to 9.5 degrees Engler at 20 C. is used.

As a thermo-setting protective lacquer, use is preferably made of the same lacquer that has been employed for providing the supporting layer. A very suitable solution consists, for example, of a mixture of an ureaformaldehyde condensation product and a non-drying alkyd resin in xylolbutanol. After mulfiing, a very hard, smooth and substantially colourless protective layer of lacquer is provided which firmly adheres to the metal mirror and which is substantially not discoloured by exposure to the atmosphere.

Example A layer of aluminium several thousandths of a millimeter thick is applied, by vaporisation in a vacuum, to a layer of hardened lacquer, mumed at 150 0., consisting of a hardened mixture of an ureaformaldehyde condensation product and a non-drying alkyd resin provided on a plate of dimensions 80 mms. by 65 mms. curved into part of a spherical surface.

The mirror is subsequently fitted to the turntable of a centrifuge, on to which is applied 1 cc. of a solution of an ureaformaldehyde condensation product and non-drying alkyd resin in a xylol-butanol mixture having a viscosity of 9 to 9.5 degrees Engler at C. On rotating the mirror rapidly the lacquer solution spreads over the metal mirror and dries to form a thin layer. This is followed by after-drying at 60 C. for

20 minutes and muffling at 115 C. for more than 1 hours. In this manner, a hard, substantially colourless well-adhering layer of lacquer having a smooth surface is formed on the metal mirror. The decrease in the reflecting power of the mirror is at most reduced only by a few percent by said layer of lacquer.

What I claim is:

1. A method of applying a protective layer to a reflecting metal surface comprising the steps of forming a base for said metal surface by providing a first non-opaque thermo-setting layer of lacquer including a non-drying alkyd resin, applying a thin layer of highly reflective metal to said first layer of hardened lacquer, and covering said metal with a second layer of non-opaque thermo-setting lacquer including a non-drying alkyd resin which is subsequently hardened at a temperature that is at least 15 C. lower than that at which said first layer of lacquer was hardened.

2. A method as claimed in claim 1 wherein the composition of said first layer of lacquer is the same as said second layer of lacquer.

4. A method of applying a protective layer to a metal surface comprising the steps of forming a base for said metal surface by providing a first thermo-setting layer of lacquer comprising an ureaformaldehyde condensation product and a non-drying alkyd resin, applying a thin layer of a metal surface comprising the steps of forming a base for said metal surface by providing a first thermo-setting layer of lacquer comprising an ureaformaldehyde condensation product and a non-drying alkyd resin, applying a thin layer of aluminum to said first layer and covering said layer of aluminum with a second layer of lacquer 3. A method as claimed in claim 1 wherein said 7 first and second layers of lacquer are distributed over said metal surface by the rapid rotation of said metal surface.

comprising an ureaformaldehyde condensation product and a non-drying alkyd resin having a viscosity of approximately 9 degrees Engler at 20 C., said second layer of lacquer being hardened at a temperature lower than that at which said first layer of lacquerwas hardened.

6. A method of applying a protective layer to a metal surface comprising the steps of forming a base for said metal surface by providing a first thermo-setting layer of lacquer comprising an ureaformaldehyde condensation product and a non-drying alkyd resin, applying a thin layer of aluminum to said first layer by vaporization in a vacuum and covering said layer of aluminum with a second layer of lacquer comprising-an ureaformaldehyde condensation product and-a non-drying alkyd resin which is subsequently hardened at a temperature which is at least 15 C. lower than the temperature at which said first layer of lacquer was hardened.

References Cited in the file of this patentv UNITED STATES PATENTS 

1. A METHOD OF APPLYING A PROTECTIVE LAYER TO A REFLECTING METAL SURFACE COMPRISING THE STEPS OF FORMING A BASE FOR SAID METAL SURFACE BY PROVIDING A FIRST NON-OPAQUE THERMO-SETTING LAYER OF LACQUER INCLUDING A NON-DRYING ALKYD RESIN, APPLYING A THIN LAYER OF HIGHLY REFLECTIVE METAL TO SAID FIRST LAYER OF HARDENED LACQUER, AND COVERING SAID METAL WITH A SECOND LAYER OF NON-OPAQUE THERMO-SETTING LACQUER INCLUDING A NON-DRYING ALKYD RESIN WHICH IS SUBSEQUENTLY HARDENED AT A TEMPERATURE THAT IS AT LEAST 15* C. LOWER THAN THAT AT WHICH SAID FIRST LAYER OF LACQUER WAS HARDENED. 